In a projection-type display apparatus, a light source device illuminates a light valve. An image signal is generated by the light valve, and is projected on a screen in an enlarged scale by a projection optical system. The projection-type display apparatus includes a light source (i.e., a light source device) that emits light, an illumination optical system that guides the light to the light valve, and the projection optical system that projects the image signal of the light valve on the screen in an enlarged scale. As the light source of the projection-type display apparatus, a high-pressure mercury lamp and a xenon lamp were mainly used. However, in recent years, projection-type display apparatuses using light sources such as LED (Light Emitting Diode) or LD (Laser Diode) have been developed.
The light sources such as the LED and the LD are dark in brightness as compared with a lamp, and therefore it is necessary to use a plurality of light sources in order to enhance to obtain a high brightness. However, when a plurality of light sources are arranged at constant intervals, a gap is formed between light fluxes emitted by respective light sources, and there is a problem that a light use efficiency decreases. That is, the gap between the light sources that occurs when arranging the respective light sources serves as a non-light emission region. The non-light emission region causes decrease in the light use efficiency. The “non-light emission region” is a region where no light flux exists.
Therefore, in a light source device disclosed by Patent Document 1, a plurality of light sources arranged in rows and columns, a plurality of reflecting mirrors (i.e., a first reflecting mirror group) corresponding to the light sources of respective rows, and a plurality of reflecting mirrors (i.e., a second reflecting mirror group) corresponding to the light sources of respective columns. That is, in Patent Document 1, a plurality of light sources are arranged in rows and columns in a plane, and the mirrors are arranged in a stepwise manner. In a proposed configuration, intervals between light fluxes in a row direction or in a column direction is eliminated, and a light flux reduced in the row direction or a light flux reduced in the column direction is emitted. Furthermore, in Patent Document 2, a configuration of a projection-type display apparatus in which stepwise reflecting mirrors arranged in a plurality of rows is proposed.